Diversity and Abundance of Denitrifying Bacteria in the Sediment of a Eutrophic Estuary

Abstract

The relationships between denitrifying microbial communities and their controlling factors are largely unknown in eutrophic estuaries sediment. This work showed that in Liaohe Estuary, nirS-type denitrifiers were consistently more abundant and diverse than nirK and nosZ-type denitrifiers, which probably means that they play an important role in nitrogen removal, particularly around nearshore stations. The dominant genera of nirK, nirS and nosZ-type denitrifiers were Sinorhizobium, Pseudomonas, and Azospirillum. Salinity, nitrogen levels, and sediment grain size were the main factors affecting the denitrification process in this eutrophic estuary. These results provide more information about the dynamics of denitrifying microbiota in marine sediments. Summary: The relationships between denitrifying microbial communities and abundance in estuaries sediment and their controlling factors are largely unknown, especially in eutrophic estuaries. In this study, nitrite reductase genes (nirS, nirK) and nitrous oxide reductase genes (nosZ) were used as molecular markers, qPCR and illumina Miseq high-throughput sequencing technology were used to study the relative abundance of key functional microflora groups and major environmental impact factors in Liaohe Estuary. The results showed that nirS-type denitrifiers were consistently more abundant and diverse than nirK and nosZ-type denitrifiers, which suggested that nirS-type denitrifiers probably play an important role in nitrogen removal in Liaohe Estuary, particularly around nearshore stations. The dominant genera of the bacterial containing nirK, nirS and nosZ genes were Sinorhizobium, Pseudomonas, and Azospirillum, in which Sinorhizobium and Azospirillum were nitrogen-fixing bacteria, while Pseudomonas was denitrogenation bacteria. The different dominant denitrifiers indicated that sedimentary denitrification was accomplished by cooperation of different denitrifying species rather than a single species. Salinity, NH4+, NO3-, NO2- and sediment grain size were regarded as determinants for the denitrification process in the sediment of the estuary. Overall, the results of this study suggest that a comprehensive analysis of different denitrifying functional genes may provide more information about the dynamics of denitrifying microbiota in marine sediments.